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Tuesday, May 14, 2013

Forest Garden Windbreak, Part 1

Thanks to the Cowlitz County Sheriff's Office Department of Emergency
Management for this visual metaphor

Yet another one to be
filed in the cluttered “we learn from our mistakes” tray. We observed, we
measured, we surveyed and we drew a lovely plan with coloured circles
representing the mature canopies of just the right amount of fruit, nut and
nitrogen-fixing trees. We thought that the first thing to plant in a forest
garden was the tree layer, especially when one considers how long it takes
trees to grow and to grow to an age when they’ll start fruiting. We now realise
that the first thing to plant in a forest garden is the windbreak.

A little snowbell tree,
Halesia carolina, never made it through its first winter and it was only after
its demise that I turned to The RHS A-Z
Encyclopaedia of Garden Plants and found that, although it’s hardy, it
should be sheltered from cold winds. The field being planted up is exposed to
the north (cold, dry winds) and the west (winds from the south west and west,
often wet).

Oft-repeated permaculture
wisdom is to observe for a year, seeing your land through four seasons before
making planning decisions. It seems strange but it’s only this winter that I’ve
become aware of just how exposed this site is and just how windy it gets.
Perhaps it’s that we sometimes only see what we want to see and are otherwise
oblivious to something staring—maybe that should be blowing—us in the face. I
notice it now. In fact, I automatically note what’s happening wind-wise each
time I visit the field … and it’s often impressive. So, we need some sort of
windbreak.

Martin talks about a
“quiet zone of protection” just behind the windbreak, followed by a turbulent
area. There is a calculation: the quiet zone “extends for seven or eight times
the height of the windbreak.” Our forest garden is 33 metres wide (E/W) and 50m
tall (N/S). That suggests our northern windbreak should be 6½m tall and the
western edge 4½m tall. We’ll use that as a guide but taper the western
windbreak towards the southern end so we don’t shade out the afternoon sun or
affect the wonderful view too much.

Martin also suggests
planting trees and shrubs that grow to the size required and therefore don’t
require onward maintenance. Nice idea, but we think that particularly difficult
to manage as trees will grow to different heights dependant on their soil and
situation, in our case being closely planted with other shrubs and trees. We
decided on a line of trees with a line of bushy shrubs in front, 1.2m between
plants and 1m between the lines, the second line offset from the first by half,
so that the shrubs block up the holes at the base of the trees.

We thought the list of plants
suggested by both books were a bit limited, so in the next blog, I’ll explain
how we chose our plants and what they are.